package demo1;

import javax.swing.tree.TreeNode;
import java.util.*;

public class Test {
    public static void main(String[] args) {
        List<Integer> list = new ArrayList<>();
        list.add(null);
        System.out.println(list.isEmpty());
        Stack<Integer> stack = new Stack<>();
        stack.push(null);
        System.out.println(stack.isEmpty());
    }

    public void levelOrder(TreeNode root) {

    }
}
//    public List<List<Integer>> levelOrder2(TreeNode root) {
//        if(root == null) {
//            return null;
//        }
//        Queue<TreeNode> queue = new LinkedList<>();
//        queue.offer(root);
////        while (!queue.isEmpty()) {
////            TreeNode cur = queue.poll();
////            List<Integer> list = new ArrayList<>();
////            list.add(cur.val);
////            if(cur.left != null) {
////                queue.offer(cur.left);
////            }
////            if(cur.right != null) {
////                queue.offer(cur.right);
////            }
//
//    }
//}
